. >>> today, presidents past and present gathered in washington, d.c. to mark the 50th anniversary of the march on washington. it was on this day in 1963, dr. martin luther king shared his dream of the american future. >> when all of god's children, black men, and white men, jews and gentiles, protestants and catholics will be able to join hands. >> more than 2,000 people heard the historic address as they crowded together on the national mall in the sweltering august heat. today's events were rich in historic symbolism, as kraig bosswell reports. >> reporter: bells range out at the let freedom ring commemoration at the exact hour dr. martin luther king jr. delivered his now famous vision. the unforgettable voice paved the way for this moment. president obama, the nation's first black president, spending exactly where dr. king stood, reflecting on the progress and the work that remains. >> no one can match king's brilliance, but the same flame that let the heart of all who were willing to take the first step for justice, i know that flame remains. >> ji